How to Install SpamAssassin with Postfix on Ubuntu

SpamAssassin is an open-source mail filter that identifies spam emails using a wide range of heuristic tests. This guide explains how to install SpamAssassin on Ubuntu 20.04 LTS or 21.04.

Prerequisites

• Deploy an Ubuntu cloud server instance at Vultr.
• Install Postfix mail transfer agent.
• Create a sudo user.
• Verify the server has outbound port 25 open.

1. Install SpamAssassin

1. Connect to your server with SSH.

2. Install SpamAssassin.

   $ sudo apt-get update
   $ sudo apt-get install spamassassin spamc -y
   

3. Add a SpamAssassin user and disable the login.

   $ sudo adduser spamd --disabled-login
   

2. Configure SpamAssassin

Assign the spamd user account to SpamAssassin and set the log and default home directories.

1. Edit the configuration settings.

   $ sudo nano /etc/default/spamassassin
   

2. Find the line:

   ENABLED=1
   

   Uncomment it by removing # and change the value from 1 to 0.

   ENABLED=0
   

3. Find the line:

   OPTIONS="--create-prefs --max-children 5 --helper-home-dir"
   

   Change it to include the SpamAssassin user account and log files directory.

   OPTIONS="--create-prefs --max-children 5 --username spamd --helper-home-dir /home/spamd/ -s /home/spamd/spamd.log"
   

4. Find the line:

   CRON=0
   

   Change the value from 0 to 1.

   CRON=1
   

5. Save and close the file.

6. Make a backup of the SpamAssassin local configuration file.

   $ sudo mv /etc/spamassassin/local.cf  /etc/spamassassin/local.cf.bk
   

7. Create a new SpamAssassin local configuration file.

   $ sudo nano /etc/spamassassin/local.cf 
   

8. Paste the information below to the file.

   rewrite_header Subject ***** SPAM _SCORE_ *****
   report_safe             0
   required_score          5.0
   use_bayes               1
   use_bayes_rules         1
   bayes_auto_learn        1
   skip_rbl_checks         0
   use_razor2              0
   use_dcc                 0
   use_pyzor               0
   ifplugin Mail::SpamAssassin::Plugin::Shortcircuit
   endif
   

9. Save and close the file.

3. Configure Postfix

1. Edit your Postfix configuration file.

   $ sudo nano /etc/postfix/master.cf
   

2. Locate these entries.

   smtp      inet  n       -       y       -       -       smtpd
   #smtp      inet  n       -       y       -       1       postscreen
   #smtpd     pass  -       -       y       -       -       smtpd
   #dnsblog   unix  -       -       y       -       0       dnsblog
   #tlsproxy  unix  -       -       y       -       0       tlsproxy
   submission inet n       -       y       -       -       smtpd
   

3. Below the smtp configuration, add a SpamAssassin content filter.

   smtp      inet  n       -       y       -       -       smtpd
   
   -o content_filter=spamassassin
   spamassassin unix -     n       n       -       -       pipe
   user=spamd argv=/usr/bin/spamc -f -e  
   /usr/sbin/sendmail -oi -f ${sender} ${recipient}
   

4. Save and close the file.

5. Restart Postfix and enable SpamAssassin to run at system startup.

   $ sudo systemctl restart postfix.service
   $ sudo systemctl enable spamassassin.service
   $ sudo systemctl start spamassassin.service 
   

More Information

To learn more about SpamAssassin, please see the official website.